The object of the present invention is a process for cutting tubes made of rigid material, notably, metal fibrocement, concrete, and plastics, particularly those having an out-of-round or oval cross-section, and means for putting said process into practice.
More specifically, the process and means contemplated by the invention make it possible not only to cut a tube but simultaneously to bevel its cut end, if necessary, to a predetermined shape. The means can be automatically adapted to the various possible diameters of the pieces to be cut without any loss of time.
French Pat. No. 79 30 754 (No. 2,471,244) describes means for cutting tubular products using radial cutting tools that are practically silent and do not release any dust. Said means remove the disadvantages (noise, dust, risk and inaccuracy) of cutting systems that make use of grinding disks. Furthermore, said means make it possible, in a simple kinematic fashion, to vary the speeds of approach, penetration, and backing off of the cutting tools relative to the axis of the tube being out, which is rotated by a revolving chuck.
However, with the cutting means described in this patent, if the tube to be cut is out-of-round or oval, the distance each cutting tool must travel to cut through the surface of the tube varies according to the radius of the oval section the tool faces, whereas progress toward the axis of rotation remains constant. The penetration of each cutting tool into the tube surface is therefore irregular, with a corresponding irregularity in the contour of the bevel obtained.
The apparatus described in French Pat. No. 76 09 87 (No. 2,306,814), which is adapted particularly to the cutting of plastic tubes includes rollers for centering the tube and a cutting tool disposed between the two upper rollers. It has the same disadvantage of irregular penetration of the edge of the cutting tool into the tube when that tube is oval or elliptical.
French Pat. No. 2,306,814 describes means adapted for cutting of pipes of various diameters in which the revolving pipe is borne by six rollers disposed coaxially to said pipe. The two lower rollers are mounted on a movable carriage that moves not radially but vertically, making it possible to move the pipe closer to or further away from the upper rollers when the diameter of the pipe is changed. The cutting tool, which is not paired with the upper rollers, is mounted on an independent support that can be moved vertically between the two upper rollers. However, the rollers are mounted in pairs, the center-to-center distance of which is fixed: a pair of upper rollers, a pair of lower rollers, and a pair of side rollers, Only the lower pair of rollers is mounted so as to move on a carriage that adjusts the pipes of different diameters by moving vertically.
When the lower rollers are moved closer to the upper rollers, there is a risk of crushing the tube into an oval shape, which is obviously a serious drawback. Furthermore, as indicated above, this prior art device does not allow an oval section of tube to be surrounded while maintaining contact with it over its entire periphery. This is due to the rigid mounting of the support rollers. In such a case, any bevel obtained will not be regular.